Everyone loses when the player base is fragmented. It’d be like if we split the NFL into two leagues. Both leagues would be worse in overall quality because neither of them would have any of the same players and neither of them would have all of the best players.
Matchmaking would be less meaningful and would take longer for BOTH groups due to there being less players in each. Even matches would be less likely to occur since there’d be a small player pool to draw from. The way people already complain about matchmaking, I can guarantee that wouldn’t go over well. There’d be many more one-sided matches. You wouldn’t be able to play with friends who were in the other competitive mode until you were ranked there, too, and your ranks would probably be different between the two modes. LFG features would be less useful if you had to make sure everyone wanted to be in the SAME competitive mode.
This is all in addition to the fact that the forced 2/2/2 mode would be about 95% DPS mains that come there expecting to finally have a mode where people will heal and tank for them, which would lead to WAY longer queues than 20 minutes. DPS queues in WoW, even at the height of it’s player count, were known to be between 30 and 45 minutes just to do a single dungeon and that’s with 3/5 of every team in that game being DPS. Imagine waiting in a 30-minute queue for a comp match and then losing. Can you imagine the salt?
There are only downsides to 2/2/2 and/or player base fragmentation, regardless of the reason for it.